1. Field of the Invention
The present invention relates to an air conditioner having a plurality of indoor units and one or more outdoor units which are connected in parallel with each other.
2. Background Art
In recent years, with improved living standards and their workability, air conditioners have come to require less and less space for their installation and also to be expected to be able to air condition a whole building. With this tendency, the demands for smaller compressors and for multi-room type air conditioners provided with a plurality of indoor units are on the increase. To meet this demand, it has been tried to stabilize the lubricating oil used in the compressors.
An air conditioner provided with a plurality of indoor units and a plurality of outdoor units connected in parallel is known from Japanese Patent Unexamined Publication No. H11-117884. A system of this type requires long piping, so that refrigerant is replenished to provide the necessary amount. However, the replenishment of the refrigerant causes the oil amount in the refrigeration cycle to be insufficient, thus lowering the ratio of the oil to the refrigerant (hereinafter, the oil dilution ratio). This damages the reliability of the compressor.
FIG. 5 is a system diagram showing a conventional air conditioner. In the refrigeration cycle, refrigerant circulates through compressor 1, condenser 2, throttle mechanism 3, an evaporator of indoor unit A and accumulator 6 in this order and returns to compressor 1. Between compressor 1 and condenser 2 is provided oil separator 7. Oil separator 7 is a device to return lubricating oil discharged to the exhaust gas from compressor 1 to compressor 1 in order to prevent a supply shortage of the lubricating oil in compressor 1, which may cause burning, and also to prevent the mixing of the oil into the circulating refrigerant, which will deteriorate the refrigerating capacity. Oil separator 7, which is a sealed container, puts the exhaust gas in the container through its inlet connected to the discharge side of compressor 1, and drops oil contained in the exhaust gas and accumulates it in the container. Oil separator 7 also discharges refrigerant gas, that is, oil-free exhaust gas through its outlet connected to the suction side of condenser 2. The oil accumulated in the container is to be returned to compressor 1 via accumulator 6 though a suction tube connected to an oil return tube in response to the detection of a predetermined liquid level from a float provided in the container.
In such an air conditioner, the use of conventional oil separator 7 allows the oil separated from the refrigerant to be returned to the compressor. However, when the type of indoor unit A is changed, a larger number of indoor units A are connected, or a plurality of outdoor units B are connected by the users request, the piping becomes longer, making it necessary to replenish the refrigerant to supply the sufficient amount. This causes the oil amount in the refrigeration cycle insufficient, making it impossible to maintain the required oil dilution ratio.